Ultra-thin shaped rubber articles such as condoms and others are generally produced by a process of using shaping molds made of glass or porcelain, a number of which shaping molds are mounted on an endless belt at determined intervals. The process comprises many steps, including a washing step of washing the shaping molds with water in a washing tank, a dipping step of dipping the shaping molds successively in a latex liquid so as to make the latex adhere to the surfaces of the shaping molds, a heat-drying step of heating and drying the latex as adhered to the surfaces of the shaping molds for curing it thereon, and an inspecting step of dipping the shaped articles as shaped with the shaping molds in an electrolytic solution for effecting pin hole inspection of the articles by applying an electric current to the solution.
However, in accordance with the conventional process, the shaped article as adhered to the surface of the shaping mold is released from the surface after the heat-drying step. The released article is then mounted on an electroconductive inspecting mold for its pin hole inspection, and it must be dipped into an electrolytic solution as it is on the mold while applying an electric current to the solution for the inspection. Since the shaped article is an ultra-thin rubber article, the operation of peeling the shaped article from the shaping mold and of re-mounting the article to the inspecting mold in the inspecting step is extremely troublesome. Therefore, the inspecting step has been a stage of seriously retarding the process of producing ultra-thin shaped articles such as condoms and others.
In order to overcome the problem, a process has been proposed in which the shaping mold is made of a metal material and the shaped article, as heat-dried and adhered to the surface of the shaping mold is directly dipped into the electrolytic solution in the inspecting step for effecting the pin hole inspection (Japanese Patent Publication No. 47-17,474). However, since the process uses a shaping mold made of a metal material, metal ions go into the latex from the shaping mold so that the condition of the colloid sol containing rubber as a dispersion medium is thereby worsened and good adhesion of the latex to the surface of the shaping mold becomes impossible, with the result that the process produces many defective articles. Because of this reason, the process has not been put to practical use.
We the present inventors have proposed, in order to overcome the above-mentioned problem, a shaping mold for producing ultra-thin shaped rubber articles, which shaping mold is made of an electroconductive ceramic material of SiC or ZrB.sub.2 or a mixture of them so that it may directly be used also as an inspecting mold as it is, whereby the troublesome operation of "peeling the shaped article from the shaping mold followed by remounting the article to a different inspecting mold" may be omitted (Japanese Patent Application Laid-Open No. 1-108,012). Using the shaping mold made of an electroconductive ceramic material, the problem that metal ions go into the latex in the dipping step may be overcome and production of ultra-thin shaped rubber articles may be effected continuously from the washing step to the successive dipping step, heat-drying step and inspecting step in order. The use of the shaping mold therefore yields a benefit of improving the production efficiency.
However, where the shaping mold is made of an electroconductive ceramic material in this way, not only the electroconductive ceramic material is high-priced of itself but also it has a large specific gravity. Therefore, the shaping mold is unsuitable for constituting a production line having therein a large amount of shaping molds as mounted on an endless belt. In addition, since the shapability of the material is bad such that the shape of the mold to be made of the material is limited. If a shaping mold having a possibly complicated shape is desired to be made of the material, polishing is needed for grinding or mirror-finishing the surface of the mold, which causes another problem of requiring much labor and cost for the grinding and mirror-finishing. Because of these reasons, the proposed shaping mold could not be said to be always satisfactory. In producing a shaping mold from an electroconductive ceramic material, a binder is incorporated into a powder of the ceramic material to prepare a compound. The compound is shaped into a non-sintered shaped body having the same shape as the intended shaping mold. The non-sintered shaped body thus obtained is then sintered at a determined sintering temperature to give the intended shaping body made of an electroconductive ceramic material, whereupon the shaped body could not be in a condition to be such an easily workable non-sintered shaped body that its surface may well be ground to have various shapes or its surface may well be polished to be a mirror-finished surface but the surface of the sintered body having a high hardness must be ground or mirror-finished by polishing.
In addition, in carrying out the process of producing ultra-thin shaped rubber articles such as condoms and others comprising the washing step, the dipping step, the heat-drying step and the inspecting step, the thickness of the shaped articles to be produced by the process is extremely small so that pin holes are easily formed in the shaped articles when the solvent is removed from the latex as adhered to the surface of the shaping mold in the heat-drying step. This is still another problem. Regarding the problem, it is not always clear as to why such pin holes are formed by what reasons, but by the present inventor's studies, it may be considered that when the heat-drying of the latex as adhered to the surface of the shaping mold is effected only by an external heat, only the surface of the layer of the latex is always dried first and thereafter the inside of the layer of the latex is to be dried successively, and that the volatile components as vaporized due to the drying of the inside of the layer of the latex would destroy the surface of the previously dried layer of the latex to go out to the outside, which would be one of the serious reasons of forming pin holes in the shaped articles. In particular, when condoms are produced by the process, the thickness of them is generally extremely small or is approximately from 0.02 mm to 0.1 mm and production of defective articles having pin holes is not allowable because of their characteristics so that the inspecting step for pin hole inspection of all the produced articles is indispensable. Therefore, in the process of producing such ultra-thin shaped rubber articles, it is also an important theme how to prevent formation of pin holes during the steps of the production and how to increase the yield of the articles.